1. Field of the Invention
The invention relates to locking devices for glad hand air brake systems for trailers.
2. Description of the Prior Art
Frequently truck drivers need to temporarily disconnect their tractors from the semi-trailers which carry cargo. The tractors and trailers almost universally utilize air brake systems. The air hoses from the trailer brake system and the tractor brake system almost universally are coupled together by means of glad hand couplers. Ordinarily, one glad hand coupler is rigidly connected to the frame of the tractor and a substantially identical glad hand coupler is connected to an air hose extending from the trailer brake system. When the two glad hand couplers are mated, a leak-free path exists between the air hoses of the truck and trailer braking system, so that high pressure (typically 90 to 120 pounds per square inch) is maintained in the systems of both the tractor and trailer. The brake mechanisms of the trailer are designed so that the trailer brakes are fully applied when there is no air pressure in the trailer brake lines (the brakes are partially or fully engaged by partial or full release of such air pressure in the brake system). Consequently, the trailer cannot be moved until the glad hand coupler of the trailer is coupled with the glad hand coupler of a tractor. However, since virtually all tractors have glad hand couplers, anyone having a tractor can merely connect it to a parked trailer, couple the glad hand coupler to that of the parked trailer, and tow it away. Pirating of parked trailers temporarily disconnected from a tractor is surprisingly commonplace. Sometimes outright theft of the trailer and its cargo occurs by "pirates". Occasionally, a shipping company by whom a truck driver is employed will realize that the truck driver is somewhat behind schedule and will send another driver (who happens to be in the vicinity of the first driver's temporarily parked trailer) to hitch a tractor to the parked trailer and finish the "haul". Then the original driver does not get paid for the remainder of the haul. This practice is strongly objected to by truck drivers, who consequently usually guard their trailers and cargoes quite carefully. It would be very helpful to truck drivers if a simple yet reliable means of locking temporarily parked cargo trailers which prevent pirates and others from removing temporarily parked cargo trailers were available at a reasonable cost.
A novelty search directed to the present invention uncovered U.S. Pat. Nos. 3,884,055; 4,039,202; 3,944,295; 3,977,221; 3,973,805 and 3,880,477. The above patents disclose the general concept of providing locking devices which prevent connecting a tractor to a trailer. However, the disclosed systems are rather elaborate, some of them involving permanently installed, complicated, and often heavy locking devices. However, none disclose a locking device for use in conjunction with glad hand brake line couplers. Other patents uncovered by this search include U.S. Pat. Nos. 2,048,353; 3,240,537; 3,285,672; and 3,674,321 disclosing various devices used in conjunction with latching or coupling systems.